1. Big data describes data stock which are to massive, to different or fast moving to use them with topical database or data-management-tools.
2. Big data are massive amounts of data from different realms, for example the internet, finance sector, energy industry, healthcare system or social media. All these data will be stored and used with special solutions.
http://wirtschaftslexikon.gabler.de/Definition/big-data.html (1.); http://www.enzyklopaedie-der-wirtschaftsinformatik.de/lexikon/daten-wissen/Datenmanagement/Datenmanagement--Konzepte-des/Big-Data (2.)